Insights into Chemical and Electrochemical Interactions between Zn Anode and Electrolytes in Aqueous Zn−ion Batteries

Abstract

Aqueous Zn-ion batteries (ZIBs) have garnered significant interest in recent years due to their potential applications in large-scale stationary energy storage. Early ZIBs research has primarily focused on searching for better cathodes and understanding cathodic Zn 2+ storage mechanisms. Only very recently has ZIBs research shifted to Zn anode. Here in this study, we report on insights into the interactions between Zn anode and aqueous Zn-salt electrolytes gained by a systematic investigation of bulk properties of electrolytes, surface properties of the reacted Zn, electrokinetics of Zn/Zn 2+ redox reaction and cycle stability of Zn/electrolyte/Zn symmetrical cells. We found that Zn metal surface, regardless of electrolyte, are always covered by a layer of Zn-containing layered double hydroxides (Zn-LDHs) upon contact with aqueous Zn-electrolytes. We show that “OH − production” pathway resulted from the dissolved oxygen in Zn-electrolytes is the root cause for the Zn-LDHs formation. The electrokinetic studies reveal that Zn/Zn(ClO 4 ) 2 interface has the highest exchange current density, while the symmetrical cell tests show that Zn(OTf) 2 is the most stable electrolyte for Zn-metal anode.